To export as WebM in Blender 2.8
CQ means constant quality, it has nothing to do with Blender, everything to do with FFmpeg which blender uses for encoding.

https://trac.ffmpeg.org/wiki/Encode/VP9

Try to use WEBM/VP9 as codec with the WEBM container. (output properties, video panel)

Depending on the platform you are working on, it should normally work right out the box.